System and method for producing block ice treated with nitrogen substitution

ABSTRACT

A system for producing block ice may include a nitrogen gas supplying unit for supplying nitrogen gas under pressure; a cooled nitrogen-dissolved water producing unit for producing nitrogen-dissolved water, which is provided with a water receiving tank for storing material water, a cooler for cooling the water stored in the water receiving tank, and a nitrogen gas injector for injecting nitrogen gas supplied from the nitrogen gas supplying unit into the water stored in the water receiving tank; and a nitrogen-substitution block ice producing unit, which is provided with a plurality of ice cans immersed in a brine tank kept at a freezable temperature for water, a filling device for filling each of the ice cans with the nitrogen-dissolved water supplied from the nitrogen-dissolved water producing unit, and a gas injector for injecting nitrogen gas supplied from the nitrogen gas supplying unit into an unfrozen portion of the nitrogen-dissolved water.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2015-098972, filed on May 14, 2015, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a system and a method for producing pillar-shaped ice, or block ice, by means of freezing water in which dissolved oxygen is substituted with nitrogen.

BACKGROUND ART

Japanese Unexamined Patent Application Publication No. 2007-155172 discloses that the surface of water in a fish hold is covered with nitrogen-gas-filled ice, which is produced by freezing water containing nitrogen gas, and that the nitrogen-gas-filled ice thaws to reduce the amount of dissolved oxygen in the water in the hold, allowing for keeping fish fresh.

Japanese Unexamined Patent Application Publication No. 2007-282550 discloses that nitrogen gas is dissolved in marinade for processing fresh food, which is then frozen in an icemaker to become ice for covering the surface of a marinade tank, and that the ice thaws to reduce the amount of dissolved oxygen in the water in the tank, allowing for enhanced protection of fresh food from oxidizing and spoiling.

Meanwhile, the maximum standardized ice commonly available in Japanese market is block ice weighing 135 kg, which is a pillar-shaped ice 280 mm long, 550 mm wide, and 1080 mm high.

Such large-sized pillar-shaped ice having over dozens of centimeters of each side, which is described herein as block ice, is produced by filling an ice can having a predetermined size with water as material and immersing the ice can in a brine tank so that brine surrounds the ice can. The brine is a solution of, for example, calcium chloride, and kept at about −8° C. to −12° C. The water in the ice can is frozen with the brine. During the time of freezing, blowing air to stir the water with an air pipe placed in the water helps bubbles and impurities existing in the water to rise and to discharge in the atmosphere as well as enhancing cooling efficiency. In order to obtain block ice with high transparency, freezing is normally performed over 36 to 72 hours.

It is known, however, that the method with aeration cannot produce highly transparent ice. Japanese Unexamined Patent Application Publication No. H6-101943 discloses a way to freeze material water while applying ultrasonic wave under negative pressure for producing transparent block ice. Japanese Unexamined Patent Application Publication No. 2011-112579 discloses a way to reduce in steps the number of revolutions of a water stirring unit provided in an ice can for producing transparent block ice.

Japanese Unexamined Patent Application Publication No. 2007-225127 discloses a way to freeze water containing micro bubbles of gas such as air, nitrogen, oxygen, carbon dioxide, or ozone, for producing gas-containing ice with bubbles being confined as they are, by which, however, transparent ice cannot be produced.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Among nitrogen-gas-filled ice currently available are block ice with a diameter of dozens of millimeters and small-sized ice crushed from plate ice with a thickness of dozens of millimeters. The art is yet to be presented to produce large-sized block ice with low concentration of dissolved oxygen while maintaining the same level of transparency as conventionally obtained.

The aeration that has been conventionally used in producing block ice serves to discharge bubbles in the water with help of stirring and upward current. Nonetheless, just replacing the conventional aeration with injection of nitrogen gas is not sufficient to produce block ice that is adequately treated with nitrogen substitution (condition in which nitrogen in exchange for oxygen is dissolved).

In view of the above problems, the present invention has an object to provide a system and a method for producing large-sized pillar-shaped ice that is adequately treated with nitrogen substitution.

Means of Solving the Problems

According to a first aspect of the present invention, a system for producing block ice that is treated with nitrogen substitution includes (a) a nitrogen gas supplying unit provided with a feeder for supplying nitrogen gas under a predetermined pressure, (b) a nitrogen-dissolved water producing unit arranged for producing nitrogen-dissolved water, which is provided with a water receiving tank for storing material water, a cooler for cooling the water stored in the water receiving tank, and a nitrogen gas injector for injecting nitrogen gas supplied from the nitrogen gas supplying unit into the water stored in the water receiving tank, and (c) a nitrogen-substitution block ice producing unit provided with a plurality of ice cans immersed in a brine tank that is kept at a freezable temperature for water, a filling device for filling each of the ice cans with the nitrogen-dissolved water supplied from the nitrogen-dissolved water producing unit, and a gas injector for injecting nitrogen gas supplied from the nitrogen gas supplying unit into each unfrozen portion of the nitrogen-dissolved water. The amount of dissolved oxygen in the nitrogen-dissolved water produced in the nitrogen-dissolved water producing unit is preferably not more than 0.3 mg/L at a temperature in the vicinity of 0° C.

In the above first aspect, the filling device for filling each of the ice cans with the nitrogen-dissolved water has a pouring tank for storing the nitrogen-dissolved water supplied from the nitrogen-dissolved water producing unit, and a plurality of pouring ports formed at the bottom of the pouring tank in such a way that each one of the ice cans is filled with the nitrogen-dissolved water through each one of the pouring ports.

According to a second aspect of the present invention, a method for producing block ice that is treated with nitrogen substitution includes a first step of producing cooled nitrogen-dissolved water that is produced by cooling stored material water while injecting nitrogen gas into the water, and a second step wherein an ice can kept at a freezable temperature for water is filled with the nitrogen-dissolved water, which is frozen while receiving injection of nitrogen gas into its unfrozen portion at least for a certain frame of time from start to finish freezing. The amount of dissolved oxygen in the nitrogen-dissolved water produced in the first step is preferably not more than 0.3 mg/L at a temperature in the vicinity of 0° C.

In the above second aspect, injection of nitrogen gas into the unfrozen portion of the nitrogen-dissolved water is stopped halfway through freezing the nitrogen-dissolved water.

In the above second aspect, a duration of time from start to finish freezing the nitrogen-dissolved water is 48 hours for producing pillar-shaped block ice measuring 280 mm long, 550 mm wide, and 1080 mm high.

Effects of the Invention

In the present invention, material water is cooled while receiving injection of nitrogen gas to produce cooled nitrogen-dissolved water, which is frozen while further receiving the injection. This makes it possible to produce block ice in which dissolved-oxygen is contained at a level fully lower than usual.

Block ice treated with nitrogen substitution, similar to small-sized nitrogen-gas-filled ice, is used to store various fresh food and other food and contributes to preserving freshness. For example, the block ice is capable of preventing and inhibiting oxidative deterioration of fresh food and capable of suppressing propagation of various bacteria. Further, large-sized block ice has many uses which small-sized ice does not have. For example, when kept in an ice chamber, the block ice itself plays a role as a cooling source. In this case, less dissolved oxygen contributes to a reduced adverse effect, compared with general ice, on its surrounding environment (e.g., fresh food kept in the ice chamber) caused by oxygen coming out when thawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a system for producing block ice treated with nitrogen substitution in accordance with an embodiment of the present invention.

FIG. 2 is a schematic view showing an example of arrangement of the nitrogen gas supplying unit shown in FIG. 1

FIG. 3 is a schematic view showing an example of arrangement of the cooled nitrogen-dissolved water producing unit shown in FIG. 1.

FIG. 4 is a schematic view showing an example of arrangement of the nitrogen-substitution block ice producing unit shown in FIG. 1.

FIG. 5 is a flowchart showing a preferred example of steps of producing block ice treated with nitrogen substitution by using the systems shown in FIGS. 1 to 4.

FIG. 6 is a photo showing a working example of block ice treated with nitrogen substitution in accordance with an embodiment of the present invention.

FIG. 7 is a photo showing conventional block ice for comparison.

DESCRIPTION OF THE EMBODIMENTS

A preferred embodiment of the present invention will be described with reference to the accompanying drawings. The block ice to which the present invention is applied is ice which can be called an “ice pillar” in the shape of a cuboid, e.g., a cube. The maximum standardized ice commonly available in Japanese market is highly transparent block ice weighing 135 kg, which is a pillar-shaped ice 280 mm long, 550 mm wide, and 1080 mm high. It should be noted that the block ice to which the present invention is applied is not limited to the ice having the above size though reference will be made hereinafter taking the ice with the above size as an example. If the length of each axis of a block ice is within the range of ±20% of that of the above standardized block ice, such block ice is considered equal to the standardized block ice. In addition, the present invention is also applied to the block ice weighing over about 20 kg.

FIG. 1 is a schematic view showing a system for producing block ice treated with nitrogen substitution in accordance with an embodiment of the present invention, in which white arrows indicates flow of gas and black arrows indicate flow of liquid (hereinafter the same convention is applied). The system for producing block ice treated with nitrogen substitution includes a nitrogen gas supplying unit 10, a cooled nitrogen-dissolved water producing unit 20, and a nitrogen-substitution block ice producing unit 30. The nitrogen gas supplying unit 10 is provided with a feeder for supplying nitrogen gas under a predetermined pressure. The cooled nitrogen-dissolved water producing unit 20 is arranged to produce cooled nitrogen-dissolved water by using material water and the nitrogen gas supplied from the nitrogen gas supplying unit 10. The nitrogen-substitution block ice producing unit 30 is arranged to produce block ice having fully-lowered level of dissolved oxygen by using the cooled nitrogen-dissolved water supplied from the nitrogen-dissolved water producing unit 20 and the nitrogen gas supplied from the nitrogen gas supplying unit 10.

The word “nitrogen substitution” of water, as used herein, is intended to define lowering a normal level of dissolved oxygen in water, which is determined in accordance with temperature under atmospheric pressure, and substituting nitrogen for the amount equivalent to the reduced dissolved oxygen. Likewise, the word “nitrogen-dissolved water” is to define the water having reduced dissolved oxygen and increased dissolved nitrogen compared with normal water, or the water in which the dissolved oxygen is substituted with dissolved nitrogen. Likewise, the words “nitrogen-substitution ice” and “ice treated with nitrogen substitution” are intended to define ice produced by freezing the nitrogen-dissolved water while maintaining the lowered level of dissolved oxygen. The lowered level of dissolved oxygen is intended to define not more than 0.3 mg/L of dissolved oxygen.

FIG. 2 is a schematic view showing an example of arrangement of the nitrogen gas supplying unit 10 shown in FIG. 1. The nitrogen gas supplying unit 10 includes an air compressor 11 for compressing atmosphere, a nitrogen gas generator 12 for extracting nitrogen gas from the compressed air, and a nitrogen gas tank 13 for storing the extracted nitrogen gas. As to the air compressor 11, for example, Oil Free “BEBICON” (Registered Trademark) of Hitachi Industrial Equipment System Co., Ltd., may be used. The compressor capable of supplying air pressure of 0.5 to 0.9 MPa is used.

In the nitrogen gas generator 12, pressed air is taken in through one end of a pressure vessel provided with a nitrogen separating membrane made of polyimide hollow fiber membrane, and oxygen is purged from an opening on the lateral side of the vessel, taking out nitrogen from the other end of the vessel. As to the nitrogen gas generator 12, which is based on different permeability rate particular to each kind of gas, for example, “Ripureru” (Registered Trademark) of KATAYAMA CHEMICAL, INC. may be used.

The nitrogen gas tank 13 is for storing nitrogen gas and provided with a regulator so as to supply the gas under a predetermined pressure. The nitrogen gas tank 13 is capable of supplying nitrogen gas separately to the cooled nitrogen-dissolved water producing unit 20 and the nitrogen-substitution block ice producing unit 30. A valve accordingly provided on respective nitrogen gas supplying lines 14 and 15 is used to switch on and off supplying nitrogen gas.

FIG. 3 is a schematic view showing an example of arrangement of the nitrogen-dissolved water producing unit 20 shown in FIG. 1. The nitrogen-dissolved water producing unit 20 includes a water receiving tank 21 for storing material water which is supplied through a water supplying line 25, a water cooler 22 for cooling water W stored in the water receiving tank 21 by means of circulation through a water circulating line 29 and a pump 23, and a nitrogen gas injecting pipe 28 for injecting nitrogen gas which is supplied from the nitrogen gas supplying unit 10 through a nitrogen gas supplying line 27.

The nitrogen gas injecting pipe 28 is, for example, a long pipe which extends horizontally in the water receiving tank 21 and has a porous wall for jetting nitrogen gas. Nitrogen gas injected into water under high pressure has an effect of raising dissolved oxygen and bubbles to release into the air upon dissolving in water. In this way, the level of dissolved oxygen in the water W in the water receiving tank 21 is lowered whereas that of dissolved nitrogen is increased, producing nitrogen-dissolved water.

The water W in the water receiving tank 21 is preferably cooled down to the vicinity of above 0° C. with the water cooler 22, enabling effective start of a freezing step later in the nitrogen-substitution block ice producing unit 30. Further, cooling the water W to the vicinity of 0° C. while injecting nitrogen gas makes it possible to suppress dissolved oxygen and to increase dissolved nitrogen compared with a normal condition in which dissolved oxygen increases in proportion to decrease in temperature.

In a working example, the nitrogen-dissolved water containing 0.3 mg/L of dissolved oxygen at the vicinity of 0° C. was obtained from the material water containing 99.7 mg/L of dissolved oxygen at room temperature by processing in the water receiving tank 21. In another working example, it was confirmed that the nitrogen-dissolved water containing 0.3 mg/L of dissolved oxygen was obtained. The amount of dissolved oxygen in normal water at 0° C. is 14.6 mg/L.

The cooled nitrogen-dissolved water in the water receiving tank 21 is supplied to the nitrogen-substitution block ice producing unit 30 through a nitrogen-dissolved water supplying line 26 and a pump 24.

FIG. 4 is a schematic view showing an example of arrangement of the nitrogen-substitution block ice producing unit 30 shown in FIG. 1. The nitrogen-substitution block ice producing unit 30 includes a pouring tank 31 for temporarily storing the cooled nitrogen-dissolved water transferred from the nitrogen-dissolved water producing unit 20 through a nitrogen-dissolved water supplying line 34, a plurality of ice cans 32 for filling with the cooled nitrogen-dissolved water, and a brine tank 33 for immersing the ice cans 32.

The pouring tank 31 is provided with a plurality of pouring ports 35 at the bottom in such a way that each one of the pouring ports is assigned to each one of the ice cans 32. Each one of the pouring ports 35 is placed right above an upper opening of each one of the ice cans 32. The pouring ports 35 are controlled to close when storing the nitrogen-dissolved water in the pouring tank 31 and to open when filling the ice cans 32 with the nitrogen-dissolved water from the pouring tank 31.

Each one of the ice cans 32 has a predetermined shape and size so as to produce one piece of block of ice, and immersed in the brine tank 33. The brine tank 33 is a tank filled with brine which is, for example, calcium chloride solution. The brine is cooled to a predetermined temperature with an external cooler (not shown). The temperature of brine to be set is adequate for freezing the nitrogen-dissolved water in the ice cans 32 to produce high-quality block ice.

In each of the ice cans 32, an injection pipe 37 is provided for injecting into the water the nitrogen gas supplied the nitrogen gas supplying unit 10 through a supplying line 36. The injection pipe 37 is, for example, a long pipe which extends vertically into the ice cans 32 and has porous walls for jetting nitrogen gas. In this way, the amount of dissolved oxygen is further decreased whereas the amount of dissolved nitrogen is increased in an unfrozen portion of the nitrogen-dissolved water in the ice cans 32 while being frozen. Injection of nitrogen gas in the ice cans 32 enables bubbles in the water to be raised and released into the air for preventing bubbles and impurities from being taken in block ice, producing highly transparent block ice. An opaque portion is often seen in the central portion of general block ice that is produced only by means of aeration; however, the block ice according to the present invention is more transparent than the general one. In addition, the effect of adequate stirring serves to enhance cooling efficiency.

FIG. 5 is a flowchart showing a preferred example of steps of producing block ice treated with nitrogen substitution by using the systems shown in FIG. 1 to 3 or 4. The size of block ice produced in the example is 280 mm long, 550 mm wide, and 1080 mm high.

First, the water receiving tank is filled with material water (Step S01). After filling, the tank may be allowed to stand for several hours to several tens of hours so as to decrease bubbles by rising and going into the air by themselves.

Second, the water in the tank is cooled to the vicinity of above 0° C. while receiving injection of nitrogen gas (Step S02). The step is carried out taking time adequate to the amount of the water for producing cooled nitrogen-dissolved water.

Next, the cooled nitrogen-dissolved water in the water receiving tank is transferred to and used to fill the pouring tank (Step S03). After filling the pouring tank, the pouring ports of the pouring tank are opened to fill the ice cans positioned thereunder with the cooled nitrogen-dissolved water (Step S04). The ice cans immersed in the brine tank are already kept at a temperature adequate for cooling, or a freezable temperature for water, by the time of filling the nitrogen-dissolved water. The freezable temperature for water is −12° C., for example.

Subsequently, the nitrogen-dissolved water in the ice cans is cooled while receiving injection of nitrogen gas into an unfrozen portion of the water. The brine tank is kept at a constant temperature until freezing is complete. In the preferred example, it takes 48 hours from start to finish freezing the nitrogen-dissolved water in the ice cans. Freezing with injection of nitrogen gas is advanced up to a certain point of time (Step S05). Preferably, the injection is continued until freezing is almost finished. When the injection is stopped, the injecting pipe is preferably taken out from the ice cans. After stopping the injection, freezing the nitrogen-dissolved water is finished (Step S06), followed by taking out of block ice that is treated with nitrogen substitution from the ice cans (Step S07).

With the freezable temperature for water, the overall freezing time, and the time of injecting and non-injecting nitrogen gas according to the above preferred embodiment, high-quality block ice that is highly transparent and sufficiently treated with nitrogen substitution can be produced. The overall freezing time in this case is shorter than that for producing conventional block ice produced by means of aeration under the same conditions in size and temperature.

The present invention is not limited to the above preferred example and the temperature of brine may be accordingly changed. Likewise, the time from start to finish freezing, the time of freezing with injection of nitrogen gas, and the time of freezing without injection of nitrogen gas may be accordingly changed as necessary. For example, under the condition of 48 hours of overall freezing time and brine temperature at −10° C., freezing may be done with injection of nitrogen gas during a first half (24 hours) of the overall freezing time whereas freezing during a latter half (24 hours) may be done without the injection. In another example, under the condition of 72 hours of overall freezing time and brine temperature at −8° C., injection of nitrogen gas is continued from starting freezing to 60 hours later, and then, the injection is stopped for last 12 hours.

FIG. 6 is a photo taken from above the block ice treated with nitrogen substitution that was produced in the steps of FIG. 5. FIG. 7 is a photo taken from above a block ice that was produced with a conventional method in the same size as the block ice shown in FIG. 6. The conventional method is to freeze normal water with aeration. Dust is filtered and removed from the air used in the aeration in the conventional method. Comparing FIG. 6 with FIG. 7 reveals that the block ice treated with nitrogen substitution is more transparent than the conventional block ice.

DESCRIPTION OF THE REFERENCE NUMERALS

-   10 nitrogen gas supplying unit -   11 air compressor -   12 nitrogen gas generator -   13 nitrogen gas tank 14, 15 nitrogen gas supplying line -   20 nitrogen-dissolved water producing unit -   21 water receiving tank -   22 water cooler -   23, 24 pump -   25 water supplying line -   26 nitrogen-dissolved water supplying line -   27 nitrogen gas supplying line -   28 nitrogen gas injecting pipe -   29 water circulating line -   30 nitrogen-substitution block ice producing unit -   31 pouring tank -   32 ice cans -   33 brine tank -   34 nitrogen-dissolved water supplying line -   35 pouring ports -   36 nitrogen gas supplying line -   37 injection pipe 

What is claimed is:
 1. A system for producing block ice that is treated with nitrogen substitution comprising: (a) a nitrogen gas supplying unit provided with a feeder for supplying nitrogen gas under a predetermined pressure; (b) a nitrogen-dissolved water producing unit for producing nitrogen-dissolved water, the nitrogen-dissolved water producing unit including a water receiving tank for storing material water, a cooler for cooling the water stored in the water receiving tank, and a nitrogen gas injector for injecting nitrogen gas supplied from the nitrogen gas supplying unit into the water stored in the water receiving tank; and (c) a nitrogen-substitution block ice producing unit including a plurality of ice cans immersed in a brine tank that is kept at a freezable temperature for water, a filling device for filling each of the ice cans with the nitrogen-dissolved water supplied from the nitrogen-dissolved water producing unit, and a gas injector for injecting nitrogen gas supplied from the nitrogen gas supplying unit into an unfrozen portion of the nitrogen-dissolved water.
 2. The system for producing block ice that is treated with nitrogen substitution according to claim 1, wherein an amount of dissolved oxygen in the nitrogen-dissolved water that is produced in the nitrogen-dissolved water producing unit is not more than 0.3 mg/L at a temperature in the vicinity of 0° C.
 3. The system for producing block ice that is treated with nitrogen substitution according to claim 2, wherein the filling device for filling each of the ice cans with the nitrogen-dissolved water comprises a pouring tank for storing the nitrogen-dissolved water supplied from the nitrogen-dissolved water producing unit, and a plurality of pouring ports formed at a bottom of the pouring tank in such a way that each one of the ice cans is filled with the nitrogen-dissolved water through each one of the pouring ports.
 4. The system for producing block ice that is treated with nitrogen substitution according to claim 1, wherein the filling device for filling each of the ice cans with the nitrogen-dissolved water comprises a pouring tank for storing the nitrogen-dissolved water supplied from the nitrogen-dissolved water producing unit, and a plurality of pouring ports formed at a bottom of the pouring tank in such a way that each one of the ice cans is filled with the nitrogen-dissolved water through each one of the pouring ports.
 5. A method for producing block ice that is treated with nitrogen substitution comprising: producing cooled nitrogen-dissolved water by cooling material water while injecting nitrogen gas into the material water; filling an ice can kept at a freezable temperature for water with the cooled nitrogen-dissolved water; and freezing the nitrogen-dissolved water while receiving injection of nitrogen gas into an unfrozen portion of the nitrogen-dissolved water at least for a selected portion of time from start to finish of freezing.
 6. The method for producing block ice that is treated with nitrogen substitution according to claim 5, wherein an amount of dissolved oxygen in the cooled nitrogen-dissolved water is not more than 0.3 mg/L at a temperature in the vicinity of 0° C.
 7. The method for producing block ice that is treated with nitrogen substitution according to claim 6, wherein injection of nitrogen gas into the unfrozen portion of the nitrogen-dissolved water is stopped halfway through freezing the nitrogen-dissolved water.
 8. The method for producing block ice that is treated with nitrogen substitution according to claim 5, wherein injection of nitrogen gas into the unfrozen portion of the nitrogen-dissolved water is stopped halfway through freezing the nitrogen-dissolved water.
 9. The method for producing block ice that is treated with nitrogen substitution according to claim 5, wherein a duration of time from start to finish of freezing the nitrogen-dissolved water is 48 hours for producing pillar-shaped block ice measuring 280 mm long, 550 mm wide, and 1080 mm high. 